Building blocks

[akist]

Hello everyone

We are starting to build a ground floor extension at the front and side of the house, and I have some questions regarding the materials.

The structural engineer has determined that the cavity walls will be made using thermalite blocks and some insulation material and with bricks on the outside.

I have said that I did not want to use these light blocks because I prefer the current construction which is all solid walls internally and cavity walls around the house, formed with concrete blocks.

He says that this would not pass thermal efficiency requirements, and he did not know how to calculate a different construction method but instead he would need to employ someone else to make different calculations, and he was confident it would result in thicker cavity walls with more insulation material.

Is this the only solution if I want to use stronger blocks, ie to have a thicker cavity with more insulation material? Can I not use special/different insulation? Do they sell any blocks that are stronger and thermally good too?

By "stronger" I mean like concrete blocks, solid and hard to drill through.

Many thanks

 

[garyo]

There's lots of flexibility - take a look at these [now out of date] wall construction options from Harringey building control (page 6 onwards) http://www.haringey.gov.uk/sites/haringeygovuk/files/u-value_guidance_nov_06a.pdf

Dense block inner leaf is unusual nowadays but you can probably do it with a 100mm cavity using the new full-fill PIR that's now available. This datasheet has a table that tells you the thermal performance in a brick+denseblock scenario: http://www.ecotherm.co.uk/Download....08AKIzWZRitqAKtjEZj3D&Bestandsnaam=Eco-Cavity

 

[Notch7]

you could use a medium density block like a fenlite maybe? Probably need additional insulation, maybe insulated plasterboard on inside.

Or you could use thermailte blocks but use sand cement render instead of bonding for plastering.

full fill is possible, although I wonder if that increased damp risk, if the detailing isnt done exactly to spec.

 

[akist]

Thanks for the guides, I have had a look and will wait to see what solution the structural engineer comes back with.